Turbine exhaust arrangement

ABSTRACT

An exhaust arrangement for a turbine is provided having an inner turbine casing, a condenser, an exhaust arrangement structure, and a bearing cone. The inner turbine casing includes a plurality of last stage buckets. A steam flow passes through the inner turbine casing and out of the plurality of last stage buckets. The condenser for receives the steam flow. The exhaust arrangement structure has a diffuser, a lower section and an upper section. The lower section has an exhaust section. The lower section receives the steam flow from the last stage buckets of the inner turbine casing through the diffuser and guides the steam flow out of the exhaust section in a direction generally towards the condenser. The upper section has a receiving section and a guiding section.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to an exhaust arrangementfor a turbine, and more specifically to an exhaust arrangement for aturbine having an exhaust arrangement structure for guiding steam flowinto a condenser.

The steam exiting the last stage buckets of a steam turbine flowsthrough a passage in a turbine casing and into a collector or exhausthood. The steam then travels into a condenser. In one type of a steamturbine having a down flow type exhaust hood, the condenser is locatedbelow the exhaust hood and the steam is directed into the condenser in agenerally downward direction. The exhaust hood typically includes anupper exhaust hood and a lower exhaust hood. A portion of the steam isdirected into the lower exhaust hood and flows directly in the downwarddirection and into the condenser. The remaining steam in the upperexhaust hood is usually guided by a steam guide located in the upperexhaust hood and into the condenser. Specifically, the steam located inthe upper exhaust hood is guided by the steam guide from a verticallyupward direction into a vertically downward direction over an innercasing of the turbine. This arrangement tends to create a vortex flowbehind the steam guide in the upper exhaust hood. The vortex flowreduces the effective flow area between the steam guide and an outerwall of the exhaust hood. The vortex flow also increases back pressurein the top portion of the exhaust hood, which in turn reduces theturbine's efficiency.

In an effort to increase turbine efficiency, the steam exiting theexhaust hood and entering the condenser should also have a generallysmooth flow. However, achieving a relatively smooth flow into thecondenser may be challenging because the steam flows in an axialdirection out of the last stage buckets, but then changes direction andflows in a radial direction into the condenser. Several approaches existto reduce or substantially eliminate the occurrence of vortex flow inthe upper exhaust hood and provide a generally smooth flow of steam intothe condenser. For example, in one approach an exhaust arrangementstructure is placed within the exhaust hood. The exhaust arrangementstructure includes a downstream channel that directs steam located inthe upper exhaust hood into the condenser. However, this approachinvolves increasing the shaft length of the turbine, and also reducesthe bearing cone foundation.

In another approach, multiple sets of vanes are placed in the exhausthood. The vanes generally direct the steam exiting the last stagebuckets from an axial direction into a radial direction. However, thevanes may not be effective at re-directing the flow of steam into theradial direction at some operating conditions. Therefore, it would bedesirable to provide a cost effective and efficient exhaust flowarrangement that directs steam in the upper exhaust hood to thecondenser.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, an exhaust arrangement for aturbine is provided having an inner turbine casing, a condenser, anexhaust arrangement structure, and a bearing cone. The inner turbinecasing includes a plurality of last stage buckets. A steam flow passesthrough the inner turbine casing and out of the plurality of last stagebuckets. The condenser receives the steam flow. The exhaust arrangementstructure has a diffuser, a lower section and an upper section. Thelower section has an exhaust section. The lower section receives thesteam flow from the last stage buckets of the inner turbine casingthrough the diffuser and guides the steam flow out of the exhaustsection in a direction generally towards the condenser. The uppersection has a receiving section and a guiding section. The receivingsection receives the steam flow from the last stage buckets of the innerturbine casing through the diffuser. The guiding section is oriented ina direction generally radially outwardly from a center axis of theturbine and is in fluid communication with the receiving section. Theexhaust section of the lower section is in fluid communication with theguiding section to direct the steam flow into the condenser. The bearingcone is positioned along the center axis of the turbine and partiallydefines the steam flow path in the lower section and the upper section.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectioned view of an exemplary steam turbine having anexhaust arrangement structure;

FIG. 2 is a cross-sectioned view of the exhaust arrangement structureshown in FIG. 1;

FIG. 3 is a perspective view of the exhaust arrangement structure shownin FIG. 1;

FIG. 4 is a bottom view of a portion of the exhaust arrangementstructure shown in FIG. 1;

FIG. 5 is a perspective view of the exhaust arrangement structure shownin FIG. 1; and

FIG. 6 is an alternative embodiment of the exhaust arrangement structureshown in FIG. 5.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an illustration of an exemplary steam turbine 10 having arotor 12, a plurality of turbine buckets 14, an inner turbine casing 16,a steam inlet 20, a condenser 22, and a guide plate that is an exhaustarrangement structure 30. In the embodiment as shown, the steam turbine10 is a down flow type steam turbine where the condenser 22 is locatedbelow the exhaust arrangement structure, and steam is directed into thecondenser 22 in a generally downward direction. In one exemplaryembodiment, the steam turbine 10 could also be a double flow steamturbine, where opposing turbine buckets could be located on oppositeaxial sides of the turbine 10 to drive the rotor 12. The inner turbinecasing 16 includes the plurality of turbine buckets 14 that provide asteam flow through the inner turbine casing 16. The steam flows out ofthe inner turbine casing 16 though a plurality of last stage buckets 32.The exhaust arrangement structure 30 is mounted to the inner turbinecasing 16. Specifically, in the embodiment as shown, the exhaustarrangement structure 30 is attached to a downstream end 34 of the innerturbine casing 16. The condenser 22 is mounted in a location that isgenerally below the exhaust arrangement structure 30 for receiving steamflow.

A diffuser 40 is created between a bearing cone 44 and steam guides 46.The diffuser 40 is located between the downstream end 34 of the innerturbine casing 16 and is part of the exhaust arrangement structure 30.The diffuser 40 is employed to guide steam out of the inner turbinecasing 16 and into the exhaust arrangement structure 30. The bearingcone 44 may include a generally frustoconical outer profile. The bearingcone 40 is placed in an axial direction that is generally parallel to acenter axis A-A of the turbine 10, and is placed on the rotor 12 andlocated within the exhaust arrangement structure 30.

The exhaust arrangement structure 30 is employed to guide a steam flow50 exiting the last stage buckets 32 of the inner turbine casing 16 andinto the condenser 22. The exhaust arrangement structure 30 includes alower section 54 and an upper section 56, a front wall 57 and an endwall 58. In the embodiment as shown, a portion of the front wall 57creates the diffuser 40. The steam flow 50 exits the last stage buckets32 flowing in a generally axial direction that may be substantiallyparallel with the center axis A-A of the turbine 10. The steam flow 50is then re-directed by the lower section 54 and the upper section 56 ofthe exhaust arrangement structure 30 into a generally radial directiontowards the condenser 22. Specifically, the lower section 54 of theexhaust arrangement structure 30 directs the steam flow 50 exiting thelast stage buckets 32 in a generally radial direction with respect tothe center axis A-A of the turbine 10, and towards the condenser 22. Alower portion 60 of the diffuser 40 and the steam guides 46 cooperatetogether to guide steam out of the last stage buckets 32 and into thelower section 54 of the exhaust arrangement structure 30. A lower outersurface 62 of the bearing cone 44 and the lower portion 60 of thediffuser 40 create a passageway 64 that defines a path for the steamflow 50. The steam flow 50 is guided though the passageway 64 and out ofthe exhaust arrangement structure 30 into the condenser 22.Specifically, an exhaust section 74 of the lower portion 54 guides thesteam flow 50 in a generally radial direction into the condenser 22.

The upper section 56 of the exhaust arrangement structure 30 includes areceiving section 70 and a guiding section 72. The upper section 56 ofthe exhaust arrangement structure 30 is in fluid communication with thelower portion 54 of the exhaust arrangement structure 30. Specifically,the exhaust section 74 of the lower portion 54 receives the steam flow50 from the upper section 56 and guides the steam flow 50 in a generallyradial direction into the condenser 22. An upper portion 76 of thediffuser 40 and the steam guides 46 cooperate to guide the steam flow 50exiting the last stage buckets 32 in an axial direction and into thereceiving section 70 of the upper section 56 of the exhaust arrangementstructure 30. An upper outer surface 78 of the bearing cone 44 and theupper portion 76 of the diffuser 40 create a passageway 80. As shown inFIG. 1, a portion of the steam flow 50 in the upper section 56 is guidedthough the passageway 80 and flows from a generally axial direction andinto a generally vertical direction away from the condenser 22. That is,the steam flow 50 flowing through an uppermost portion 81 of the upperportion 56 of the exhaust structure 30 (shown in FIGS. 1-3) is orientedin a generally vertical direction away from the condenser 22.

Turning now to FIGS. 2-3, the exhaust arrangement structure 30 isillustrated. FIG. 2 is a side view of the exhaust arrangement structure30. The exhaust arrangement structure 30 includes a front end 82 thatattaches to the downstream end 34 of the inner turbine casing 16 (FIG.1). The lower section 54 and the upper section 56 are each locatedbetween the front wall 57 and the end wall 58. FIG. 3 is a perspectiveview of the exhaust arrangement structure 30. Referring now to FIGS.1-3, the guiding section 72 of the upper portion 56 is in fluidcommunication with and receives the steam flow 50 from the receivingsection 70. The guiding section 72 is oriented to guide the steam flow50 in a radial direction. Specifically, the steam flow 50 is guided in adirection that is oriented generally radially outwardly from the centeraxis A-A of the turbine 10. The exhaust section 74 of the lower section54 is in fluid communication with and receives the steam flow 50 fromthe guiding section 72 of the upper section 56. The guiding section 74directs the steam flow into the condenser 22 (shown in FIG. 1). FIGS.2-3 also illustrate the steam flow 50 being guided out of the lowersection 54 of the exhaust arrangement structure 30.

The vortex flow that occurs in conventional down flow exhaust hoods isreduced or substantially eliminated in the steam flow 50 located in theupper section 56 of the exhaust arrangement structure 30. Also, flowdiffusion of the steam flow 50 in the upper section of the exhaustarrangement structure 30 is typically increased when compared toconventional down flow exhaust hoods. Increased flow diffusion usuallyresults in a reduction of back pressure of the turbine, which results ingreater turbine efficiency. Moreover, the exhaust arrangement structure30 may be less expensive and complex when compared to some down flowhoods that are currently available. This is because the outer casing ofthe hood can be omitted, as the exhaust arrangement structure 30 acts asa guide to receive the steam flow from the last stage buckets 32 of theinner turbine casing 16. The exhaust arrangement structure 30 can besupported directly by a foundation of the turbine 10 (not shown), whichresults in enhanced machine reliability. Some approaches that arecurrently available may reduce vortex flow in a conventional exhausthood, however some of these approaches involve increasing the shaftlength of the turbine. Increasing the shaft length of the turbine willin turn increase the overall axial dimensions of the turbine. Incontrast, the exhaust arrangement structure 30 does not substantiallyincrease the length of the turbine 10.

Turning now to FIG. 4, a bottom view of a portion of the exhaust flowarrangement structure 30 is shown. The steam flow 50 enters the exhaustflow arrangement 30 at an inlet 94 located at the front end 82. A flowdiffusion portion 90 of the exhaust arrangement structure 30 isindicated by a phantom line. The flow diffusion portion 90 of theexhaust arrangement structure 30 represents where flow diffusion of thesteam flow 50 occurs. This is because a remaining portion 92 of theexhaust flow structure 30 is generally located within the inner turbinecasing 16 (which is shown in FIG. 1), and therefore flow diffusion ofthe steam flow 50 can not typically occur. The flow diffusion portion 90of the exhaust flow arrangement 30 has a height H that is measuredbetween the end wall 58 of the exhaust arrangement structure 30 and anouter surface 97 of the exhaust arrangement structure 30. The height Hcan be adjusted depending on the particular system requirements of theturbine 10. Specifically, an increased height H of the portion 90results in a greater Effective Area Ratio (EAR). The EAR is the ratiobetween the inlet 94 of the exhaust arrangement structure 30 and anoutlet 96 (shown in FIG. 1) of the exhaust arrangement structure 30. Agreater EAR results in greater pressure recovery of the steam flow 50that flows through the exhaust flow arrangement 30.

FIGS. 5-6 illustrate a portion of the outer profile of the exhaustarrangement structure 30. Turning now to FIG. 5, in one embodiment, theflow diffusion portion 90 of the exhaust arrangement structure 30includes an edge surface 98. Turning now to FIG. 6, in an alternativeembodiment of an exhaust arrangement structure 130, a flow diffusionportion 190 may include a filleted edge 198 instead. The filleted edge198 represents where the inner wall (not shown) of the exhaustarrangement structure 130 corresponds to the filleted edge 198. That is,an inner wall of the exhaust arrangement structure 130 includes agenerally curved profile. The inner wall may also include othernon-rectangular cross-sections as well, such as, for example, anelliptical profile. The curved profile may be used in an effort toenhance the flow characteristics of the exhaust arrangement structure130.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. An exhaust arrangement for a turbine, comprising: an inner turbinecasing including a plurality of last stage buckets, a steam flow passingthrough the inner turbine casing and out of the plurality of last stagebuckets; a condenser for receiving the steam flow; an exhaustarrangement structure comprising: a diffuser for guiding the steam flowout of the plurality of last stage buckets of the inner turbine casing;a lower section having an exhaust section, the lower section receivingthe steam flow from the plurality last stage buckets of the innerturbine casing through the diffuser and guiding the steam flow out ofthe exhaust section in a direction generally towards the condenser; anupper section having a receiving section and a guiding section, thereceiving section receiving the steam flow from the plurality of laststage buckets of the inner turbine casing through the diffuser and theguiding section oriented in a direction generally radially outwardlyfrom a center axis of the turbine and in fluid communication with thereceiving section, and the exhaust section of the lower section in fluidcommunication with the guiding section to direct the steam flow into thecondenser; and a bearing cone positioned along the center axis of theturbine and partially defining the steam flow path in the lower sectionand the upper section.
 2. The exhaust arrangement of claim 1, whereinthe exhaust arrangement structure is attached to a downstream end of theinner turbine casing.
 3. The exhaust arrangement of claim 1, comprisinga plurality of steam guides, wherein the diffuser and the steam guidescooperate together to guide the steam flow out of the plurality of laststage buckets of the inner turbine casing.
 4. The exhaust flowarrangement of claim 1, wherein the bearing cone is positioned withinthe exhaust arrangement structure, and partially defines the lowersection and the upper section.
 5. The exhaust flow arrangement of claim1, wherein the exhaust arrangement structure includes a flow diffusionportion, wherein flow diffusion of the steam flow occurs within the flowdiffusion portion.
 6. The exhaust flow arrangement of claim 5, whereinthe flow diffusion portion includes a height that is measured between anend wall of the exhaust arrangement structure and an outer surface ofthe exhaust arrangement structure.
 7. The exhaust flow arrangement ofclaim 6, wherein the height is adjustable depending on the systemrequirements of the turbine.
 8. The exhaust flow arrangement of claim 7,wherein increasing the height results in a greater Effective Area Ratio(EAR), and wherein the EAR is the ratio between an inlet of the exhaustarrangement structure and an outlet of the exhaust arrangementstructure.
 9. The exhaust flow arrangement of claim 1, wherein a portionof an outer surface of the exhaust arrangement structure includes afilleted edge, and wherein an inner wall of the exhaust arrangementstructure corresponds to the filleted edge.
 10. The exhaust flowarrangement of claim 1, wherein the turbine is a double flow steamturbine.
 11. A steam turbine, comprising: an inner turbine casing havinga downstream end and including a plurality of last stage buckets, asteam flow passing through the inner turbine casing and out of theplurality of last stage buckets; a condenser for receiving the steamflow; an exhaust arrangement structure attached to a downstream end ofthe inner turbine casing, the exhaust arrangement structure comprising:a diffuser for guiding the steam flow out of the plurality of last stagebuckets of the inner turbine casing; a lower section having an exhaustsection, the lower section receiving the steam flow from the pluralityof last stage buckets of the inner turbine casing through the diffuserand guiding the steam flow out of the exhaust section; an upper sectionhaving a receiving section and a guiding section, the receiving sectionreceiving the steam flow from the plurality of last stage buckets of theinner turbine casing through the diffuser and the guiding sectionoriented in a direction generally radially outwardly from a center axisof the turbine and in fluid communication with the receiving section,and the exhaust section of the lower section in fluid communication withthe guiding section to direct the steam flow into the condenser; and abearing cone positioned along the center axis of the and within theexhaust arrangement structure, the bearing cone partially defining thesteam flow path in the lower section and the upper section.
 12. Thesteam turbine of claim 11, comprising a plurality of steam guides,wherein the diffuser and the steam guides cooperate together to guidethe steam flow out of the plurality of last stage buckets of the innerturbine casing.
 13. The steam turbine of claim 11, wherein the exhaustarrangement structure includes a flow diffusion portion, wherein flowdiffusion of the steam flow occurs within the flow diffusion portion.14. The steam turbine of claim 13, wherein the flow diffusion portionincludes a height that is measured between an end wall of the exhaustarrangement structure and an outer surface of the exhaust arrangementstructure.
 15. The steam turbine of claim 14, wherein the height isadjustable depending on the system requirements of the turbine.
 16. Thesteam turbine of claim 15, wherein increasing the height results in agreater Effective Area Ratio (EAR), and wherein the EAR is the ratiobetween an inlet of the exhaust arrangement structure and an outlet ofthe exhaust arrangement structure.
 17. The steam turbine of claim 11,wherein a portion of an outer surface of the exhaust arrangementstructure includes a filleted edge, and wherein an inner wall of theexhaust arrangement structure corresponds to the filleted edge.
 18. Thesteam turbine of claim 11, wherein the turbine is a double flow steamturbine.
 19. A steam turbine, comprising: an inner turbine casingincluding a plurality of last stage buckets, a steam flow passingthrough the inner turbine casing and out of the plurality of last stagebuckets; a condenser for receiving the steam flow; an exhaustarrangement structure comprising: a diffuser for guiding the steam flowout of the plurality of last stage buckets of the inner turbine casing;a lower section having an exhaust section, the lower section receivingthe steam flow from the plurality of last stage buckets of the innerturbine casing through the diffuser and guiding the steam flow out ofthe exhaust section; an upper section having a receiving section and aguiding section, the receiving section receiving the steam flow from theplurality of last stage buckets of the inner turbine casing through thediffuser and the guiding section oriented in a direction generallyradially outwardly from a center axis of the turbine and in fluidcommunication with the receiving section, and the exhaust section of thelower section in fluid communication with the guiding section to directthe steam flow into the condenser; a flow diffusion portion where flowdiffusion of the steam flow occurs, the flow diffusion portion includinga height that is measured between an end wall of the exhaust arrangementstructure and an outer surface of the exhaust arrangement structure, theheight being adjustable depending on the system requirements of thesteam turbine; and a bearing cone positioned along the center axis ofthe and within the exhaust arrangement structure, the bearing conepartially defining the steam flow path in the lower section and theupper section.
 20. The steam turbine of claim 19, comprising a pluralityof steam guides, wherein the diffuser and the steam guides cooperatetogether to guide the steam flow out of the plurality of last stagebuckets of the inner turbine casing.